By default, the program tclsh8.5 is called, but an alternative program may be provided as an optional argument to (tk-start). For a distributable application, you can bundle tclkit with your application, and call the tclkit application in tk-start.

Under windows, there is a problem with keyboard input. Currently, the fix is to show a dialog box which is dismissed by pressing 'Enter' (not clicking!) directly after starting tk.